This invention relates generally to a lubricant and spotting fluid; and method for lubricating and/or dislodging a stuck drill string or casing during downhole drilling operations, and more particularly to an aqueous-based spotting fluid and lubricant comprised of a glycol or glycol ether based on long chain epoxides (e.g. C.gtoreq.3 and more preferably .gtoreq.10). A preferred composition in accordance with this invention is the reaction product between the epoxide of 1-hexadecene and 2-ethylhexanol.
During drilling operations the drill string may become stuck and cannot be raised, lowered, or rotated. One mechanism for causing this problem is known as differential sticking.
Differential sticking may be defined as the sticking of the drill string against a permeable formation containing less pore fluid pressure than the hydrostatic pressure exerted by the drilling fluid column and usually occurs when the drill string remains motionless for a period of time. The mechanism by which this occurs involves the drill string coming into contact with the permeable zone, remaining quiescent for a period of time sufficient for mud cake to build up on each side of the point of contact, thus sealing the pipe against the borehole. The annular pressure exerted by the drilling fluid then holds the pipe against the borehole or the permeable zone.
Freeing of differentially stuck pipe is essentially a matter of reducing this pressure differential which exists across the pipe. One method used simply involves a reduction in fluid pressure by replacing the annular fluid with a less dense fluid allowing for less pressure differential to exist between the borehole and annulus. In some cases the borehole pressure may exceed the annular pressure which in turn allows the pipe to be blown away from the borehole.
One commonly used method to release stuck pipe is the use of a "spotting" fluid in the hole opposite the stuck section of pipe. The spotting fluid may penetrate between the mud cake and pipe lubricating the area between the pipe and borehole resulting in less friction and quicker release. More often than not, an extensive period of time is necessary for this to occur which results in an expensive loss of rig time.
As mentioned above, spotting fluids were developed to lubricate the affected area, "spotting" referring to the placement of a quantity of drilling fluid known as a pill or slug containing a release agent at the area of concern. Furthermore, incorporating a lubricating factor into the drilling mud during ordinary operation to prevent drill pipe sticking is a common practice.
The composition of these release agents has generally consisted of various kinds of oils such as synthetic oils, vegetable oils, mineral oils, diesel oils and crude oils. Oil-based spotting fluids, however, are generally difficult to prepare because strong agitation is required to achieve an oil-water suspension taking much time when time may be a crucial consideration.
Disposal of drilling fluids containing oil components has also come under much closer environmental scrutiny and regulation concurrent with increasing concern about reducing pollutants in ground water and coastal water environments. Drilling muds containing oil are generally classified as pollutant streams having costly regulated disposal procedures. Such oils are not in the best interest of marine wild life and may leave an unsightly sheen in the water.
Accordingly, there is an urgent need for a spotting fluid release agent and lubricant in the art of oil and gas production which is nontoxic, non-oil based, inexpensive and easy to prepare and use.
Examples of non-oil based spotting fluids and lubricants proposed are found in U.S. Pat. Nos. 4,964,615; 5,002,672; 5,120,708; 5,127,475; 4,230,587; 4,466,486; 4,494,610; 4,614,235; and 4,659,486. U.S. Pat. No. 4,964,615 to Mueller et al describes a composition for freeing jammed drill strings and pipes which utilizes a fatty acid alkyl ester or mixtures of esters as well as at least one thickener and at least one emulsifier. In a preferred embodiment, the Mueller et al patent describes the use of ester of oleic acid with 2-ethyl hexanol as a preferred fatty acid alkyl ester for use in the spotting fluid described therein.
U.S. Pat. Nos. 5,002,672 and 5,127,475 to Hayes et al both describe an aqueous-based spotting fluid composition which utilizes a glycerophosphoric acid ester and a diacetyltartaric acid ester of mono and/or diglycerides. U.S. Pat. No. 4,230,587 to Walker discloses a stuck drill pipe spotting fluid comprising polyethylene glycol while the Walker U.S. Pat. No. 4,466,486 utilizes a stuck drill pipe spotting fluid comprising a polymer (cellulose or polyethylene oxide). The Walker U.S. Pat. No. 4,494,610 utilizes an alcohol based spotting fluid while U.S. Pat. No. 4,614,235 lo Keener et al is an ether based spotting fluid employing an alkylene glycol ether of the class consisting of alkylene glycol ether, poly (alkylene glycol) ether and mixtures thereof. U.S. Pat. No. 4,659,486 to Harmon discloses a polyester based drilling fluid. One notably successful attempt at overcoming the deficiencies of the prior art is the water-based drilling fluid additive composition sold by BH INTEQ Fluids Technology division of Baker Hughes, Incorporated of Houston, Tex. under the trademark AQUA MAGIC, the composition of which is described in detail in U.S. Pat. No. 5,120,708, assigned to the assignee hereof and fully incorporated herein by reference. The drilling fluids additive of U.S. Pat. No. 5,120,708 comprises (a) a water soluble polyoxyalkylene compound selected from polyoxyalkylene glycols, monoalkylethers of polyoxyalkylene glycols, and mixtures thereof in combination with (b) a water dispersible particulate asphalt.
Notwithstanding the foregoing description of water-based drilling fluid additives, there continues to be a need for water-based drilling fluid components and additives which exhibit improved environmental properties such as biodegradability and low toxicity without sacrificing functional operability such as the provision of lubrication and/or spotting. While glycols and glycol ethers are water-based and are known and used for drilling fluid additives, such compositions continue to suffer from serious drawbacks and deficiencies. This is because glycols and glycol ethers, when suggested for use as drilling fluid additives, have been based either on ethylene oxide or propylene oxide chemistry. Additives based on ethylene oxide such as described in U.S. Pat. No. 4,230,587 to Walker exhibit several deleterious properties including poor efficiency, foaming, undesirable toxicity levels and health hazards and are relatively expensive. Additives based on propylene oxide are often not sufficiently biodegradable to meet regulatory requirements.